Magmatic-hydrothermal processes in Haman, Gunbuk and Daejang Cu deposits, Korea

초록

Cu deposits located in south-eastern part of Korean Penninsula. Cretaceous shale are intruded by series of Cretaceous granodiorites of plutonic-porphyritic textures. The shale around the intrusions are metamorphosed to hornfels. The three Cu deposits have common veining and alteration features: (1) early barren stage of pervasive propylitic alteration, cut by (2) ore-bearing quartz veins with amphibole-potassic alterations, and (3) the latest barren calcite veins. Tourmaline-magnetite-pyrrhotite-chalcopyrite occur in the ore-bearing quartz veins of the Haman deposit. Magnetite-pyrrhotite-chalcopyrite-arsenopyrite occur in the Gunbuk deposit and pyrite-chalcopyrite-galena-sphalerite occur in the Daejang deposit. Quartz veins contain three types of fluid inclusions: (1) aqueous inclusion, (2) vapor-rich inclusion, and (3) brine inclusion. Occurrences of coexisting vapor-brine inclusion in the assemblage indicates fluid phase separation. The homogenization temperatures (Th) are 190-590, 200-470, and 320-460 ℃ in the Haman, the Gunbuk, and the Daejang, respectively. Paleo-depths estimated by hydrostatic pressure regime are about 5, 3 and 3 km in the Haman, the Gunbuk, and the Daejang deposits, respectively. The quartz veins and fluid inclusions were analysed by LA-ICP-MS. Similar Al and Ti concentrations in the quartz of the Haman and the Gunbuk indicate comparable pH and T conditions in the hydrothermal fluids. Metal concentrations in fluids stay constant with changing P-T condition, which indicate that metal precipitation at the current exposure may not be significant. We suggest that the Haman deposit formed near deep intrusion center with focused high-T fluid flow. The Gunbuk and the Daejang deposits might be formed at relatively shallower periphery. Based on the reconstructed magmatic-hydrothermal processes in the three deposits, we speculate that a high-grade orebodies might be denudated at the current surface level.